Process of producing cellulose esters



Patented Jan. 16, 1934 sis PRGCESS OF PRODUCING CELLULOSE ESTERS Henri Louis Barthelemy, Milan, Italy, assignor to Ruth Aldo Company (Inc.), New York, N. Y., I a corporation of New York No Drawing. Application July 28, 1927, Serial No. 209,166, and in France December 28, 1926 6 Claims.

It is already known from scientific and patent literature that the esterification of cellu ose, and of nitrocelluloses which have a low content of nitrogen and have been specially prepared for the purpose, may be effected by treatment with an anhydride, either undiluted or diluted with suitable solvents, in the presence of a catalyst. The catalyst may consist of a strong mineral acid; of acid salts, such as alkali bisulphates; normal salts with an acid reaction, such as copper sulphate. or zinc chloride; free halogens, such as chlorine, bromine, iodine; acid chlorides, such as phosphorus oxychloride; or organic compounds, such as sulphuric esters, hydrazinesul phate, hydroxylaminesulphate, and so on.

per minute respectively,

These catalysts are intended to produce simultaneously a partial depolymerization and a change of state of the cellulose complex.

Various applications of one and the same cata- 0 lyst have already been patented.

In studying this delicate question of the acetylation of cellulose it has been ascertained that the application of one and the same process may result in the production of esters of en- 5 tirely different qualities according to the chemical treatments to which the cellulose has been previously subjected, which treatments are generally unknown to the manufacturer who buys the cotton already bleached. From two batches of the same cotton, one of which, for example, had been bleached with permanganate (copper value 0.67) and the other with sodium hypochlorite (copper value 1.86) the viscosities of the acetate products were 104/100 and 64/100 and the breaking strengths 8.070 kg. and 5.73 kg. per sq. mm.

Attempts were then'made to find a process by means of which a greater regularity in the quality could be attained at will even when starting with cotton of different kinds, and without the necessity of subjecting the cotton to a preliminary chemical treatment necessitating the re-damping and re-drying of the material.

The present invention is based upon the discovery that it is quite possible to vary the course of the acetylation of cotton without having to modify the process or the various quantities of the reagents. All that is needed is to add to the customary catalyst, for instance sulfuric acid, a

substance which elfects a very slight oxidation of the fibres during the esterification. This oxidation can be regulated at will by accurately proportioning the amount of such addition.

This association of the catalyst with the aux- 5 iliary substance produces a kind of mixed catalysis, the ordinary hydrolysis effected by the catalyst when used alone being here replaced by a simultaneous oxidation and hydrolysis of the fibre.

Contrary to a priori expectation, themechanical and plastic properties of the resulting cellulose acetate do not suffer by suchtreatment, but are retained in a high degree provided a well devised working method be employed, such for instance as that hereinafter described, an ex press condition being that the amount of active oxygen employed does not exceed 0.3% of the weight of the cotton.

It has also been ascertained that the acetate obtained by suitable treatment is far whiter than that obtainable from the corresponding strongly bleached cotton. This is a further novel and considerable advantage if the acetate is to be converted into brightly colored plastic materials or into artificial silk.

The following oxidation agents, for example, may be employed in conjunction with an ordinary catalyst: Manganese sulfates; manganic acetate; chromic acid; monopersulfuric acid, so-called Caro acid; manganic acid and permanganic acid; peracetic acid; and so on.

These acid substances are obtained by decomposing-preferably at a temperature of about 0 C.their alkali salts with the theoretical quantity of sulfuric acid in an acetic acid medium. The following may serve as examples of the application of the process:

Example I 18 kg. of cotton are swollen by the action of 25 kg. of glacial acetic acid in a suitable apparatus. After a suitable time depending on the hardness of the fibre, the apparatus is charged with a first bath composed of 72.5 kg. of 21% acetic anhydride, in a suitable solvent such as acetic acid and 10 kg. of the following mixture:-

- Grams Commercial sodium bichromate 150 Sulfuric acid (density 1.84) 650 Glacial acetic acid 9200 and continuously added during a period not exceeding an hour.

If the apparatus is properly insulated, the heat developed by the exothermic reaction suffices to produce, in a few hours, a clear solution of the cellulose acetate in acetic acid. The cellulose acetate is then partially saponified by known methods.

After flocculation has occurred, a thorough Washing is given, in order to remove the chromium salts.

Example II The bath specified in Example I is replaced by a bath consisting of 69 kg. of 23% acetic anhydride in a suitable solvent, such as acetic acid and 10 kg. of the following mixture:

Grams Pulverized sodium permanganate Sulfuric acid (density 1.84) 6'75 Glacial acetic acid 9245 organic acids as solvents and a complex catalyst consisting of a strong mineral acid and an oxidizing agent for the cellulosic material.

2. The process for the esterification of cellulose by means of organic acid anhydrides; consisting in effecting the esterification in the presence of organic acids as solvents, and a complex catalyst formed by associating a known esterifying catalyst with an amount of an oxidizing agent capable of providing not more than 0.3% of active oxygen based on the Weight of the cellulose.

3. The process for the esterification of cellulose by means of organic acid anhydride; consisting in effecting the esterification in the presence of organic acids as solvents, and a complex catalyst consisting of sulfuric acid and an oxidizing agent for the cellulosic material.

4. The process for the esterification of cellulose by means of organic acid anhydrides; consisting in effecting the esterification in the presence of organic acids as solvents, and a complex catalyst consisting of sulfuric acid and a chromic acid.

5. The process for the acetylation of cellulose by means of acetic anhydride; consisting in effecting the acetylation in the presence of acetic acid as solvent, and a complex catalyst consisting of sulfuric acid and an oxidizing agent for the cellulosic material. I

6. The process for the acetylation of cellulose by means of acetic anhydride'; consisting in effecting the acetylation in the presence of acetic acid as solvent, sulfuric acid and chromic acid.

HENRI LOUIS BAR'IHELEMY. 

